Oil prices at four-year highs have triggered concerns about demand as U.S. President Donald Trump has blamed the Organization of the Petroleum Exporting Countries for rising gasoline prices for American consumers.

Prices have eased slightly after Saudi Arabia and Russia said they would raise output to at least partly make up for expected disruptions from Iran, OPEC's third-largest producer, due to the sanctions that take effect on Nov. 4.

But the pull-back did little to dent a 15-20 percent rise in oil prices since mid-August, which has pushed them to their highest since 2014.

Washington wants governments and companies around the world to stop buying Iranian oil from Nov. 4 to put pressure on Tehran to renegotiate a nuclear deal.

However, India will buy 9 million barrels of Iranian oil in November, two industry sources said, indicating that the world's third-biggest oil importer is to continue purchasing crude from the Islamic republic.

Many analysts say they expect Iranian exports to drop by around 1 million barrels per day (bpd).